For example, for use in a DC brushless motor, a stator has been adopted, which is constructed by assembling a substantially T-shaped core in an annular form, having an arcuate yoke section and pole sections that extend diametrically to an inner side thereof from the yoke section.
This type of stator is manufactured by clamping and rotating the yoke section of the core about a spindle shaft, and while a wire material, which is supplied from a supply bobbin, is guided by a nozzle, and by being reciprocally operated in an axial direction (spindle shaft direction) of the pole sections (winding frame), a multi-layered winding coil is produced on the pole sections.
Generally, the wire winding device for producing the coil is equipped with a supply bobbin that supplies the wire material, a coil producing section that produces the coil by winding the wire material on the winding frame (core), and a tensioning mechanism arranged between the supply bobbin and the coil producing section for alleviating variations in tension that occur upon winding the wire material on the winding frame.
When the wire material is wound on the winding frame, because the wire material becomes stretched if the tension is too high, or slacking occurs if the tension is too low, it is essential that the tension be maintained at an appropriate value.
As a tensioning mechanism, there has been adopted a mechanism that absorbs tension variations using a spring or a damper, or a mechanism in which the wire material is wound on a brake roller, which adjusts the braking force of the brake roller responsive to a tension that is estimated from the wire material length, or the like.
However, with such a tensioning mechanism using a spring or a damper, because the tension adjustment range is determined arbitrarily by the spring constant, the capability to suppress tension variations is low. On the other hand, with the brake roller mechanism, because the wire material is made to intersect and is trained around the roller multiple times, when the supply bobbin is replaced, time is required for resetting and performing maintenance thereon.
In Japanese Laid-Open Patent Publication No. 11-222357, there is disclosed a wire winding device comprising a spool (wire material source) that feeds out a wire material, a spindle that retains a winding frame on which the wire material is wound, a spindle motor for rotatably driving the spindle, a detecting means for detecting a supply amount of the wire material to the winding frame, and a control means for controlling the feed-out speed of the wire material from the wire material source so that the supply amount of the wire material to the winding frame, which is detected by the detecting means, and the wire material feed-out amount agree with each other.
With the technique disclosed in Japanese Laid-Open Patent Publication No. 11-222357, by means of a feed-out motor arranged at the spool, a tensioning mechanism can be simplified, which alleviates variations in tension by controlling the feed-out amount of the wire material. Even without using a tensioning mechanism such as a brake roller mechanism, variations in tension can be suppressed reliably.